The typical automated process for making a masonry unit comprises the steps of placing a mold which is open at the top and bottom on a solid pallet, filling the mold with a suitable composite material (generally comprising cement and aggregate material), vibrating the filled mold and/or the pallet while simultaneously compacting the material within the mold via a compression head inserted into the top of the mold to densify the composite material, stripping the molded composite material (still resting on the pallet) from the mold, and curing the molded composite material to form a masonry unit.
It is now also common to split off a portion of the cured masonry unit so as to create a decorative face on the unit. The splitting process creates an irregular texture, and exposes, and may actually break, some of the aggregate material in the composite. The face created by the splitting process is often referred to in the industry as "split face", or "rock face".
The splitting of cured masonry units by this process involves additional equipment and manufacturing steps. In order to avoid the added costs associated with the splitting process, there have been efforts to alter the configuration of the mold so as to achieve the same "split face" texture on the masonry unit without the additional splitting steps.
For example, U.S. Pat. No. 3,981,953 describes a mold in which a plurality of patterning elements are suspended in a frame in a horizontal array below and parallel to the compression head of the molding machine. These elements are positioned to correspond with a desired pattern of lines on the finished product. A plurality of smaller rods, arrayed at right angles to the patterning elements may also be mounted in the frame. After the mold box is filled, the compression head is lowered into the mold box, thus burying the patterning elements in the composite material. Upon stripping of the mold, retraction of the compression head pulls off the top layer of composite material, which is held between the head and the patterning elements. The result is that the pattern of the array of elements is impressed on the top of the masonry unit. Between the marks left by the patterning elements, a roughened texture is produced. This arrangement produces a pattern on the top face of the masonry unit, as molded.
There are a number of applications, however, when the face of the unit that must be textured is not the top face of the unit as molded, but, rather, is one of the vertical side faces of the unit. The '953 patent describes a modification of the process, where the frame holding the array of patterning elements is inserted vertically into the mold along and parallel to one side wall of the mold. The mold is filled and vibrated. When the molded masonry unit is stripped from the mold, it is stripped with the frame holding the array of patterning elements still embedded in the molded unit. After stripping, the frame and array of elements is pulled away from the vertical face of the molded unit in a direction normal to the face, pulling a portion of the molded unit away at the same time to expose the pattern on the vertical side of the molded unit, with roughened areas between the pattern lines. Thus it is an extremely cumbersome and impractical process to achieve a roughened texture on a vertical side of the masonry unit as cast with the process of the '953 patent. And whether the treated surface is the top or side of the masonry unit, the composite material has to be cleaned from the array of patterning elements after each cycle of the machine.
U.S. Pat. No. 3,940,229 describes a process for achieving a roughened texture on the vertical side of a masonry unit as molded. The patent describes a mold in which a small lip is formed on the inner, lower edge of a vertical wall of the mold. As the densified, composite material is stripped from this mold, the lip moves vertically up the side wall of the masonry unit, and tears some of the composite material away from the main mass. The lip temporarily retains this composite material in place against a portion of the mold wall as the mold is stripped. The retained material is thus dragged, or rolled, up the face of the main mass as the mold is stripped, creating a random, roughened texture on the vertical side face of the masonry unit. An improvement on this process is described in U.S. patent application Ser. No. 08/748,498, filed Nov. 8, 1996, which is assigned to the same assignee as the present application.
The process of the '229 patent, and the improved process of the '498 application retain a small amount of material against the mold wall as the mold is stripped. These processes create a rough textured face on a concrete masonry unit, but the texture can have a "shingled" appearance.
Another example of an alternative to splitting is shown in U.S. Pat. Nos. 5,078,940 and 5,217,630. The molds described in these patents make use of a lower lip on a vertical wall of the mold, similar to that shown in the '229 patent. In addition, the molds employ a plurality of projections on the associated vertical mold wall above the lip, and a vertically oriented reinforcing mesh above the lip and inboard from the wall. This combination of reinforcing mesh and projections is similar to the array of patterning elements and normally-oriented rods described in the '953 patent. When the mold is initially filled, the composite material fills in between the mesh and the wall, and around the projections. When the mold is vibrated, the material is compacted. The combination of lip, mesh and projections holds a large mass of compacted, composite material against the mold wall as the mold is stripped. These patents show the retained mass of composite material shearing from the rest of the composite material, to create a roughened face on the molded unit that is stripped from the mold.
In the process of the '940 and '630 patents, the use of the projections (whether or not in combination with a reinforcing mesh) holds a much larger mass of material against the mold side wall than is the case in the '229 process, and does so in such a fashion as to retain that material in the mold from cycle to cycle. This creates what is perceived to be a potential drawback of the process of the '940 and '630 patents: it is not self cleaning, and it can be difficult and/or time consuming to clear the retained material from the mold side wall, which apparently need not be done on every machine cycle, but must be done periodically. On the plus side, this process can create a face which does not evidence as much "shingling" as with the '229 process.
Accordingly, there is a need for a self-cleaning mold assembly which will produce a random, roughened texture face that does not evidence any "shingling" on a vertical side face of a masonry unit without a splitting step, so that the manufacturing process can operate without periodic cleaning or maintenance for extended production runs.